One vertex per element, one color per generator, with an edge from x to x·s.
(9,10)(11,18)(12,16)(13,22)(14,17)(15,21)(19,24)(20,23)(27,33)(28,36)(30,37)(32,38)(34,39)(35,40) involution — undirected(1,2,4,5)(3,7,8,6)(9,11)(10,15)(12,19)(13,20)(14,21)(16,23)(17,18)(22,24)(25,26)(27,34)(28,32)(29,31)(30,35)(33,39)(36,38)(37,40)(2,5)(6,7)(9,12,14,13)(10,16,17,22)(11,19,21,20)(15,23,18,24)(25,27,28,33,29,35,36,40)(26,30,32,37,31,34,38,39)(9,13,14,12)(10,16,17,22)(11,20,21,19)(15,23,18,24)(25,26)(27,34)(28,32)(29,31)(30,35)(33,39)(36,38)(37,40)(1,3,4,8)(2,6,5,7)(11,21)(15,18)(19,20)(23,24)(26,31)(30,34)(32,38)(37,39)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.